Interest in the architectural work of Charles Rennie Mackintosh has been granted an extensive amount of attention which has only increased after the partial loss of the west wing to fire in May 2014. However, even in the broad compilation of literature, hardly any attention has been afforded to his stained glass. The following work set out to explore the role of stained glass in the Mackintosh Building at the Glasgow School of Art through an investigation into his formative influences. Insight into the intentions and narratives behind his stained glass only becomes comprehensible if understood within a wider context, incorporating his influences, artwork and attitudes. It was found that there was a commonality throughout his narratives permeating his work. This inferred that his use of stained glass in this significant building was as a testing ground for the synthesis of his ideological attitudes and influences. The restoration is generating new insight into overlooked aspects of his designs, renewing the interest in Mackintosh, and curiously redefining many widely held beliefs.